As a general rule, it's hard to change one's skiing by changing the position of the hands. More often, the position of the hands is a symptom of something else. You can't blame your coaches because sometimes a focus on the hands/poles can easily drive a subconscious change to other movements. For example, the drill where you rest the poles on the tops of your hands and carry them by "leveling" often does a great job at getting the hips and shoulder to stay parallel to the slope surface through induced leg movements. Another example is how lifting ones hands prior to pole touch while powder skiing can help induce extension unweighting. But if you are the point where several coaches have told you to get your hands higher that probably means the "just do it" approach isn't going to work.
If you stand with your hands at your sides, just lifting them vertically to your armpits isn't going to help you see them. If you keep your arms straight and lift your hands up, they will trace an arc upward and forward and you'll probably be able to spot them in your peripheral vision soon after they pass belt high. Try this move just bending from the elbows. When your arms get to a 90 degree angle, your hands should be just out of peripheral vision (you can look down and seem them, but that's cheating!). But if you bend at the ankles as you are moving your hands, then your hands will end up a couple inches more forward and you should be able to just barely see them. If you then add a little upper arm swing so that your elbows move forward 2-3 inches the hands should come clearly into view. Effective pole use incorporates all 3 of these movements: the hands moving up and forward, the elbows moving forward and the ankle movement to move the hips forward. Try thinking of the hands as pulling the hips forward. My bet is that your coaches don't just want your hands higher. They probably also want your weight to be moving "forward" at initiation as well. An on snow drill I'd recommend is skiing with your hands held behind your back. The intent here is that you will either automatically compensate with ankle movement or you will get a much stronger (Yikes!) sensation of being in the back seat.
If your poles are too long that can cause you to carry your hands too high and vice versa. Few people have poles that are too short. But as long as your looking at poles, you should take this opportunity to double check your pole length. The old standby of holding the pole at the basket end at a 90 degree angle is being challenged by a more modern method (which escapes my memory at the moment) which suggests a slightly shorter pole length (I remember it as effectively the old way with your boots on and down one notch from there - hopefully someone else has also heard about this). It could be that your poles are too long and that's why using them feels awkward.